Trocar for inserting implants

ABSTRACT

An implant retention trocar includes a cannula for puncturing the skin of an animal and an obturator for delivering the implant beneath the skin of the animal. The implant retention trocar has a cannula distal tip design which causes a minimum of trama and tearing of tissue during implant insertion. A spring element received within the cannula prevents an implant which is to be inserted into an animal from falling out of the cannula during the implant insertion process. The spring element includes a longitudinal leg which is folded with a zig-zag shaped bend. When the spring element is inserted into the cannula the zig-zag shaped bend of the longitudinal leg retains the implant within the cannula.

This application claims priority based on U.S. Provisional ApplicationNo. 60/082,759 filed Apr. 23, 1998, which is incorporated herein byreference in its entirety.

FIELD OF THE INVENTION

The invention relates to a tubular member for inserting drug-containingdevices into animals and more particularly, the invention relates to atrocar for inserting implants.

BACKGROUND OF THE INVENTION

Many different types of delivery systems for delivering beneficialagents such as pharmaceuticals for the prevention, treatment, anddiagnosis of disease are known in the art. One type of delivery systemis the subcutaneous implant which contains a supply of a beneficialagent and is implanted beneath the skin of an animal to deliver thebeneficial agent over time. Some of the different types of subcutaneousimplants include osmotic drug delivery implants, dissolvable or erodablepellet type implants, and diffusional implants. Some examples of osmoticdelivery implant systems are described in U.S. Pat. Nos. 4,111,202;4,111,203; and 4,203,439.

The process of placing subcutaneous osmotic implants and other types ofimplants under the skin is often performed by use of a trocar systemwhich is a two-piece system, including a cannula and an obturator. Withthis system, an incision is first made through the skin of the patientand the cannula and obturator are inserted together through the skin.The obturator is then withdrawn leaving the cannula in place as a guidefor inserting the implant. The implant is inserted through the bore ofthe cannula while the obturator is used to push the implant to the endof the cannula. The obturator is then used to hold the implant in astable axial position while the cannula is being withdrawn from thepatient to deposit the implant in a known position in the channelpreviously occupied by the cannula. The cannula and obturator are thenwithdrawn completely leaving the implant in place beneath the skin.

This method of insertion of an implant, including the step of removal ofthe obturator for insertion of the implant through the cannula followedby reinsertion of the obturator increases the possibility that sterilityof the implant site will be compromised during these steps. However, itis difficult to insert the implant into the cannula prior to insertionof the cannula into the patient because the implant will tend to failout of the cannula during the insertion process.

Known trocars can also be used with the implant in the trocar duringinsertion, however this method relies upon the skilled and careful useby the health care practitioner to orient the trocar so as to employgravity to retain the implant in the cannula. Alternatively, implantscapable of distortion may be held in a cannula by interference with awall of the cannula to keep the implant in place against the force ofgravity.

Known balling guns have been used in veterinary implantation procedureswhich retain the implant or bolus tablet in a cannula by either aninterference fit or a distortion of the cannula. However, the cannulasare generally complex and expensive to manufacture.

Accordingly, it would be desirable to provide a trocar system in whichan implant may be retained within the cannula in a simple and economicalmanner during insertion of the cannula into a patient and the implant iseasily pushed out of the cannula and into the patient.

SUMMARY OF THE INVENTION

The trocar system according to a preferred embodiment of the presentinvention includes a cannula retaining spring element which is fixed toan inside surface of the cannula to retain an implant within the cannulauntil the implant is to be delivered by pressure applied by anobturator.

According to one aspect of the present invention, a trocar includes acannula for receiving an implant and inserting the implant into ananimal, a spring element received within the cannula, and an obturatorfor delivering the implant from the cannula into the animal. The springelement has a leaf spring for retaining the implant inside the cannula.The leaf spring applies a frictional force against the implantsufficient to prevent the implant from sliding out of the cannula underthe weight of the implant.

In accordance with an additional aspect of the invention, a trocarincludes a substantially cylindrical cannula body, a distal end of thecannula body having a leading edge formed by a first plane which is at afirst angle with respect to a longitudinal access of the cannula body,and a trailing edge formed by a second plane which is at a second anglewith respect to the longitudinal access of the cannula body. The firstangle of the leading edge is larger than the second angle of thetrailing edge.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in greater detail with reference to theaccompanying drawings, in which like elements bear like referencenumerals, and wherein:

FIG. 1 is a top view of a spring element according to the presentinvention prior to bending of the leaf spring;

FIG. 2 is a perspective view of the spring element of FIG. 1 with theleaf spring bent;

FIG. 3 is a perspective view of the spring element of FIGS. 1 and 2which has been bent in an arch for insertion into a cannula;

FIG. 4 is a cross-sectional side view of a portion of a cannula of FIG.3, taken along line 4—4, with the spring element according to thepresent invention inserted within the cannula;

FIG. 5 is a side cross-sectional view of the cannula and leaf springelement of FIG. 4 with an implant and obturator inserted in the cannula;

FIG. 6 is a side view of a first embodiment of the cannula tip;

FIG. 7 is a side cross-sectional view of the cannula tip of FIG. 6;

FIG. 8 is a side view of a cannula tip according to an alternativeembodiment of the invention;

FIG. 9 is a side cross-sectional view of the cannula tip of FIG. 8;

FIG. 10 is a side cross-sectional view of a prior art cannula tip withan implant inside the cannula; and

FIG. 11 is a side view of the cannula of FIG. 9 with an implant shown attwo different positions inside the cannula.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The implant retention trocar according to the present invention includesa cannula and an obturator for implanting beneficial agent deliverydevices in animals. According to one embodiment the cannula may be usedto puncture a foil or other covering material of a sterile sealedimplant package. Alternatively, the implant package may be opened byscrewing, tearing, or cutting. The cannula then may be used to removethe implant from the package or the implant may be placed in the cannulaby hand or with forceps. The implant is delivered to an implantationsite within an animal, generally just beneath the skin, by the trocar byapplying pressure to the obturator. The implant retention trocar causesa minimum of trauma and tearing of tissue during implant insertion.

A first aspect of the invention relates to a spring element 10 receivedwithin the cannula of the trocar to prevent an implant which is to beinserted into an animal from falling out of the cannula during theimplant insertion process. Another aspect of the invention relates tothe shape of the distal end of the cannula which prevents trauma andtearing of tissue during implant insertion.

The spring element 10 is shown in a finished configuration in FIG. 3 asit is inserted into a cannula 20. The spring element will be describedwith respect to FIGS. 1-3 according to the steps by which the springelement is formed. As shown in FIG. 1, the spring element is formed froma thin sheet of metal, such as a stainless steel, titanium, aluminum,copper, or other appropriate spring metal. The sheet is substantiallyrectangular in shape with a continuous cut 14 forming a T-shaped leafspring 12. The cut 14 may be made in any known manner such as bypunching or photoetching. The leaf spring portion 12 of the springelement 10 has a longitudinal leg 16 and a cross leg 18 extendingsubstantially perpendicular to the longitudinal leg. The spring element10 may be punched, photoetched, laser cut, or formed in any other knownmethod.

As shown in FIG. 2, the longitudinal leg 16 is folded with a zig-zagshaped bend. When the spring element 10 is inserted into a cannula it isthe zig-zag shaped bend of the longitudinal leg 16 which will retain theimplant within the cannula. The cross leg 18 of the leaf spring 12 iswider than the longitudinal leg 16 in the circumferential direction andprovides tabs on either end which 25 secures the leaf spring againstmotion away from the cannula surface toward the cannula axis. Bending ofthe longitudinal leg 16 in the zig-zag shape has the effect ofshortening the distance from the cross leg 18 to an attachment point 22where the longitudinal leg meets the rest of the spring element. Onceshortened, end portions or tabs of the cross leg 18 lie along thesurface of the spring element plate guiding the bent longitudinal leg.The cross leg 18 is slidable in a direction parallel to the cannula axisalong the cylindrical surface of the cannula as the zig-zag shapedlongitudinal leg 16 is extended and retracted. The ends of the cross leg18 keep the longitudinal leg 16 properly oriented so that thelongitudinal leg does not block loading of the implant into the cannula.The number and angle of the bends in the longitudinal leg 16 may bevaried as needed to achieve implant retention.

FIG. 3 illustrates the spring element 10 once it has been bent about alongitudinal axis into an arch shape for insertion into the cannula 20.The radius of curvature of the arched spring element 10 is preferablyapproximately the same as or slightly smaller than a radius of thecannula 20 in which the spring element will be inserted. Once the springelement 10 is placed within the cannula 20, the spring element ispreferably fixed inside the cannula by a sterilizable adhesive, such ascyanoacrylate, epoxy, polyester, acrylic, or other adhesive. Theadhesive is preferably both biocompatible and compatible with thebeneficial agent inside the implant to be delivered by the trocar. Thespring element 10 may also be fixed inside the cannula by other knownmethods such as welding, laser welding, electric resistance welding, orthe like.

Once the spring element 10 has been fixed within the tip of the cannula20 and an implant has been inserted into the cannula, the zig-zagconfiguration of the longitudinal leg 16 exerts a force between anexternal surface of the implant and an internal surface of the cannulato retain the implant in the cannula until it is expelled by axialsliding of the obturator by the user. Cross sectional views of thecannula 20 and spring element 10 are shown in FIGS. 4 and 5 with andwithout an implant 30 and obturator 32. As can be seen from the figures,the amount of bend of the longitudinal leg 16 is decreased by theinsertion of the implant causing the implant to be retained in thecannula by the spring retention force of the longitudinal leg.

FIG. 5 illustrates a distal end of an obturator 32 according to thepresent invention having a tapered exterior end surface 36 to preventthe spring element 10 from being expelled by motion of the obturator. Inparticular, the distal end of the obturator has a frusto-conical shapewhich prevents the obturator from becoming caught on either the edge 34of the spring element 10 or on the edge of the cross leg 18.

Although the spring element 10 has been described as formed of a metalmaterial, the spring element may also be formed of another springmaterial such as plastic, in the shape described above. The springelement 10 may be formed of plastic by molding, extruding, cold forming,thermo forming or a combination of these processes. In addition, theshape of the leaf spring 12 can be modified without departing from theinvention. For example, the cross leg 18 of the leaf spring can beformed in any shape as long as it is somewhat larger in width than thelongitudinal leg 16. The longitudinal leg 16 may also take on othershapes such as a tapered shape, as long as the leg has sufficient lengthform the formation of one or more bends.

The spring element 10 according to the present invention retains theimplant within the cannula without requiring the grinding of specialretention features into the cannula inner wall which would requireexpensive secondary operations. The retention spring element 10according to the invention can be produced economically by punching,photoetching, or laser cutting and can be inserted in an automatedfashion. Thus, the implant retention trocar can be inexpensivelyproduced as a single-use device formed of recyclable materials.

The preferred embodiments of the cannula tip illustrated in FIGS. 6-11in combination with the spring element described above provide animproved, easy to use and economical trocar. The cannula tip 40 shown inFIG. 6 includes a distal end having a changing profile between a leadingedge 42 and a trailing edge 44 of the distal end opening 46 of thecannula. In particular, when viewed in profile, as shown in FIG. 6, thedistal end of the cannula is cut by a first plane 48 and by a secondplane 50. The first plane 48 forms an angle θ₁ with a longitudinal axisof the cannula and the second plane 50 forms and angle θ₂ with thelongitudinal axis. The angle θ₁ is about 10 to 60 degrees, preferably 20to 40 degrees, and the angle θ₂ is about 5 to 45 degrees, preferably 5to 25 degrees. A difference between the angles θ₁ and θ₂ is betweenabout 2 and 50 degrees, preferably between about 6 and 35 degrees.

A transition section 52 of the cannula distal end between the firstplane 48 and the second plane 50 is preferably a gradual or blendedtransition rather than an abrupt transition. A gradual transitionaccording to the present invention may be a slight rounding just at theintersection between the first and second planes. Alternatively, thegradual transition may include a curved surface extending along up toabout one third of the distal end opening. This transition section 52 islocated within either a central or top third of the cannula between thetop and bottom of the cannula. The transition section provides a slightprotruding bump which assists in spreading tissue during cannulainsertion.

The two different angles θ₁, and θ₂ at the distal end of the cannulaaccording to the present invention provide reduced tissue trauma andtearing during the trocar insertion. In particular, the relativelyshallow angle at the trailing edge 44 of the cannula 40 avoids coring ortearing tissue during insertion of the cannula and also avoids coringwhen the cannula is used to puncture it's own foil packaging or thepackaging of an implant.

As shown in FIG. 7, the trailing edge 44 of the cannula distal end ispreferably fully radiused to prevent tissue from catching on thistrailing edge during implant insertion. The radiused edge 44 alsoprevents coring of tissue by preventing a complete plug of tissue frombeing cut by the cannula. The radiused trailing edge 44 is blended outaround the circumference of the cannula with the radiused portioncompletely blended out at a blend end 54 which is located within thecentral third of the cannula.

FIGS. 8, 9, and 11 illustrate an alternative of a cannula tip 60 for usewith the trocar according to the present invention. The cannula tip 60has an angled distal end for inserting the cannula into tissue whichincludes a leading edge 62 and a trailing edge 64 of the cannula. Asdescribed above, the profile of the distal end includes an angle whichis smaller near the trailing edge 64 than near the leading edge 62. Thischanging angle of the cannula tip profile helps to avoid tearing orcoring of tissue during trocar insertion.

The cannula tip 60 is provided with a leading edge 62 having a reversegrind 66 around approximately one half of the circumference of thecannula. The reverse grind 66 is formed by a grinding operation whichcreates a beveled exterior surface of the cannula. The reverse grind 66causes the leading cutting edge 68 of the cannula to be moved from theexterior diameter of the cannula to an interior diameter of the cannula.An angle α between the longitudinal axis of the cannula 60 and thesurface of the reverse grind 66 is approximately 5 to 60 degrees,preferably 20 to 45 degrees. Although the reverse grind 66 isillustrated as having a planar cross-section, the grind may also have aslightly convex or concave cross-section.

One of the advantages of the reverse grind is illustrated by acomparison of FIGS. 10 and 11. In FIG. 10, a cannula 80 according to theprior art is illustrated with an implant 82 shown in hidden lines. Ifthe implant 82 protrudes slightly from the cannula 80 during insertion,it can be seen that a gap 84 is present in which tissue can becometrapped. This gap 84 of the prior art cannula increases the trauma andtearing of tissue due to trapping of tissue during implant insertion.However, with the reverse grind 66 shown in FIG. 11, the cannula leadingcutting edge 68 having the reverse grind forces the tissue away from theimplant 82 rather than into a gap between the implant and the cannulapreventing tissue entrapment and possible implant jam.

Another advantage provided by the reverse grind 66 involves the improvedcannula insertion due to the ability of the angled surface to pushtissue apart during insertion. This angled or tapered surface of thereverse grind reduces tissue trauma and tearing. In addition, thereverse grind 66 improves tracking of the cannula. For example, aconventional cannula having an angle cut distal end as shown in FIG. 10will track at an angle with respect to the axis of the cannula due tothe angle distal end. However, the reverse grind 66 of the presentinvention provides a restoring force during cannula insertion whichhelps the cannula track along a substantially axial path.

FIG. 11 also illustrates a leading edge of an implant 82 a positioned ata preferred position inside the cannula 60 for implantation. The implant82 a may be held at this position during implantation by the obturatoror by another holding means. When the forward end of the implant 82 a ispositioned between the leading cutting edge 68 and the trailing edge 64of the cannula as shown in FIG. 11 the implant edge will help to forcethe tissue apart reducing trauma and tearing of the tissue andpreventing coring. According to a preferred implantation method, theimplant 82 a is positioned within the cannula with a forward end of theimplant located between ⅓ and ⅔ of the way between the leading cuttingedge 68 and the trailing edge 64.

The cannulas 20, 40, 60 according to the present invention may be formedof any of the known cannula materials such as plastic or metal. Theretention trocar may be a single use device or may be reusable. Thecannulas and trocars according to the present invention are intended forinsertion of implants in animals including humans, livestock, and thelike.

While the invention has been described in detail with reference to thepreferred embodiments thereof, it will be apparent to one skilled in theart that various changes and modifications can be made, and equivalenceemployed, without departing from the spirit and scope of the invention.

1. A trocar comprising: a cannula for receiving an implant and insertingthe implant into an animal, the cannula having a sharp tissuepenetrating distal end; a spring element received entirely within thecannula, the spring element having a leaf spring for retaining theimplant inside the cannula, the leaf spring applying a frictional forceagainst the implant sufficient to prevent the implant from sliding outof the cannula under a weight of the implant, wherein the spring elementis formed as a sheet with the leaf spring formed as a T-shaped cut outportion within the sheet; and an obturator for delivering the implantfrom the cannula into the animal.
 2. The trocar according to claim 1,wherein the leaf spring has a longitudinal leg and cross leg, and thecross leg of the leaf spring is wider than the longitudinal leg in acircumferential direction.
 3. The trocar according to claim 2, whereinthe cross leg has tabs on either end which secure the leaf springagainst motion away from a surface of the cannula towards an axis of thecannula.
 4. The trocar according to claim 1, wherein the sheet issubstantially rectangular.
 5. A trocar comprising: a cannula forreceiving an implant and inserting the implant into an animal; a springelement received within the cannula, the spring element having a leafspring for retaining the implant inside the cannula, the leaf springapplying a frictional force against the implant sufficient to preventthe implant from sliding out of the cannula under a weight of theimplant; an obturator for delivering the implant from the cannula intothe animal; and wherein the leaf spring has a plurality of successivebends and the successive bends are arranged to alternatively contact aninside wall of the cannula and an outside of the implant to retain theimplant in the cannula.
 6. The trocar according to claim 5, wherein theleaf spring has a longitudinal leg arranged substantially parallel to anaxis of the cannula and a cross leg substantially perpendicular to thelongitudinal leg, and the plurality of successive bends are formed onthe longitudinal leg.
 7. The trocar according to claim 5, wherein theleaf spring having the plurality of successive bends is compressed in aradial direction of the cannula by insertion of the implant into thecannula.
 8. The trocar according to claim 5, wherein the obturator has atapered distal end to prevent ejection of the spring element from thecannula when the obturator is moved distally to eject the implant fromthe cannula.
 9. The trocar according to claim 5, wherein the springelement is fixed within the cannula.
 10. A trocar comprising: a cannulafor receiving an implant and inserting the implant into an animal; aspring element received within the cannula, the spring element formedfrom a sheet with a continuous cut forming a T-shaped leaf springconnected to a surrounding sheet; an obturator for delivering theimplant from the carnula into the animal; and wherein the leaf springretains the implant inside the cannula by applying a frictional forceagainst the implant sufficient to prevent the implant from sliding outof the cannula under a weight of the implant.
 11. The trocar accordingto claim 10, wherein the obturator has a tapered distal end to preventejection of the spring element from the cannula when the obturator ismoved distally to eject the implant from the cannula
 12. The trocaraccording to claim 10, wherein the spring element is fixed within thecannula.
 13. The trocar according to claim 10, wherein the leaf springis received entirely within the cannula.
 14. The trocar according toclaim 10, wherein the spring element is received entirely within thecannula.
 15. The trocar according to claim 10, wherein the sheet issubstantially rectangular.